/*
* Protective (legacy) MBR.
*
* This MBR contains standard DOS partition table with a single partition, type
* of 0xEE. The partition usually encompassing the entire GPT drive - or 2TiB
* for large disks.
*
* Note that Apple uses GPT/MBR hybrid disks, where the DOS partition table is
* synchronized with GPT. This synchronization has many restriction of course
* (due DOS PT limitations).
*
* Note that the PMBR detection is optional (enabled by default) and could be
* disabled by BLKID_PARTS_FOPCE_GPT flag (see also blkid_paertitions_set_flags()).
*/
static int is_pmbr_valid(blkid_probe pr)
{
int flags = blkid_partitions_get_flags(pr);
unsigned char *data;
struct dos_partition *p;
int i;
if (flags & BLKID_PARTS_FORCE_GPT)
goto ok; /* skip PMBR check */
data = blkid_probe_get_sector(pr, 0);
if (!data)
goto failed;
if (!is_valid_mbr_signature(data))
goto failed;
p = (struct dos_partition *) (data + BLKID_MSDOS_PT_OFFSET);
for (i = 0; i < 4; i++, p++) {
if (p->sys_type == BLKID_GPT_PARTITION)
goto ok;
}
failed:
return 0;
ok:
return 1;
}
static int parse_dos_extended(blkid_probe pr, blkid_parttable tab,
uint32_t ex_start, uint32_t ex_size, int ssf)
{
blkid_partlist ls = blkid_probe_get_partlist(pr);
uint32_t cur_start = ex_start, cur_size = ex_size;
unsigned char *data;
int ct_nodata = 0; /* count ext.partitions without data partitions */
int i;
while (1) {
struct dos_partition *p, *p0;
uint32_t start, size;
if (++ct_nodata > 100)
return 0;
data = blkid_probe_get_sector(pr, cur_start);
if (!data)
goto leave; /* malformed partition? */
if (!is_valid_mbr_signature(data))
goto leave;
p0 = (struct dos_partition *) (data + BLKID_MSDOS_PT_OFFSET);
/* Usually, the first entry is the real data partition,
* the 2nd entry is the next extended partition, or empty,
* and the 3rd and 4th entries are unused.
* However, DRDOS sometimes has the extended partition as
* the first entry (when the data partition is empty),
* and OS/2 seems to use all four entries.
* -- Linux kernel fs/partitions/dos.c
*
* See also http://en.wikipedia.org/wiki/Extended_boot_record
*/
/* Parse data partition */
for (p = p0, i = 0; i < 4; i++, p++) {
uint32_t abs_start;
blkid_partition par;
/* the start is relative to the parental ext.partition */
start = dos_partition_start(p) * ssf;
size = dos_partition_size(p) * ssf;
abs_start = cur_start + start; /* absolute start */
if (!size || is_extended(p))
continue;
if (i >= 2) {
/* extra checks to detect real data on
* 3rd and 4th entries */
if (start + size > cur_size)
continue;
if (abs_start < ex_start)
continue;
if (abs_start + size > ex_start + ex_size)
continue;
}
par = blkid_partlist_add_partition(ls, tab, abs_start, size);
if (!par)
goto err;
blkid_partition_set_type(par, p->sys_type);
blkid_partition_set_flags(par, p->boot_ind);
ct_nodata = 0;
}
/* The first nested ext.partition should be a link to the next
* logical partition. Everything other (recursive ext.partitions)
* is junk.
*/
for (p = p0, i = 0; i < 4; i++, p++) {
start = dos_partition_start(p) * ssf;
size = dos_partition_size(p) * ssf;
if (size && is_extended(p))
break;
}
if (i == 4)
goto leave;
cur_start = ex_start + start;
cur_size = size;
}
leave:
return 0;
err:
return -1;
}
